While myths have been debunked, more research is needed on carpal tunnel syndrome

Orthopedics Today, June 2015

Although carpal tunnel syndrome is common, noted surgeons who spoke with Orthopedics Today believe there is still debate about the best treatment options for patients and whether there is more about the condition to be discovered.

“The reason that people are willing to take a look at new [treatments for carpal tunnel] is because not everyone is happy after carpal tunnel release,” David C. Ring, MD, chief of hand surgery at Massachusetts General Hospital, told Orthopedics Today. “Some people with advanced disease — constant numbness, weakness, atrophy — those people have permanent nerve damage and it can be very disappointing when they have the surgery and they still have those problems. It does not get better, and so they are unhappy.”

According to Asif Ilyas, MD, program director of the hand and upper-extremity fellowship at the Rothman Institute, carpal tunnel syndrome is a common issue, with studies quoting general prevalence in the 3% to 7% range.

“Carpal tunnel syndrome, in general, is an area of intense research for a number of reasons,” Ilyas, who is also an associate professor of orthopedic surgery at Thomas Jefferson University, said. “One, it is a problem that we as hand surgeons treat very regularly and two, it is a condition that affects a large swath of the population and can significantly affect their lives as well as their livelihood.”

David C. Ring, MD, noted that according to the best available evidence, idiopathic median neuropathy at the wrist is genetic..

Image: Robert Carlin Photography

Research also continues to be warranted on the best way to diagnose carpal tunnel syndrome, which, according to A. Lee Osterman, MD, is still widely debated.

“The optimal diagnosis of carpal tunnel is somewhat debated, whether you rely on just symptoms and signs alone in the physical examination, whether you include electrodiagnostic testing [or] whether you do both,” Osterman, head of the Philadelphia Hand Center and professor of hand surgery and orthopedics at Thomas Jefferson University, said. “Most people still use both clinical examination and the diagnostic tests … but, the American Academy of Orthopaedic Surgeons’ recommendation was, while there was no best scientific evidence to support the use of electro-studies, that they were often helpful.”

Patients who are diagnosed with carpal tunnel syndrome tend to be between the ages of 40 years and 60 years, noted Osterman, although there are some individuals in their 70s and 80s who have fairly severe carpal tunnel that has not been treated. Patients with certain health conditions or who have experienced hand trauma can also suffer from carpal tunnel syndrome.

Amy L. Ladd, MD, chief of the Chase Hand Center and professor of orthopedic surgery at Stanford University Medical Center, noted patients with thyroid disease or those who have had kidney transplants, as well as patients with amyloidosis, are also at higher risk for carpal tunnel syndrome.

“The more common demographic [for carpal tunnel syndrome] is women more than men, although non-exclusively,” Ladd said. “We tend to see it at hormonal fluctuations with women, things like pregnancy, birth control [or] menopause.”

However, Barry P. Simmons, MD, chief of the Hand and Upper Extremity Service at Brigham & Women’s Hospital, told Orthopedics Today 75% to 80% of carpal tunnel syndrome found in women ages 50 years to 55 years is idiopathic. According to Ring, idiopathic carpal tunnel leads researchers to believe that carpal tunnel syndrome is a genetic issue.

“The best evidence for etiology is that [carpal tunnel syndrome] is a genetic problem,” Ring, who is also a professor of orthopedic surgery at Harvard Medical School, said. “The only question left is, ‘Are there any epigenetic factors?’ Is there anything that people do: anything they eat, any activity they do that might increase their risk beyond what their genes have given them? To date, there are no proved epigenetic factors [in idiopathic carpal tunnel syndrome].”

Surgical treatments

Performing carpal tunnel release surgery can help relieve symptoms of carpal tunnel syndrome and can be performed endoscopically or by dividing the transverse carpal ligament, according to Osterman and Ring.

“We understand that the course of [carpal tunnel syndrome] can be modified. You can change the natural history by dividing the transverse carpal ligament,” Ring said. “So if you cut the ligament, the carpal tunnel is bigger and then not only will the symptoms be relieved, but [the patient] will be out of the woods in terms of developing atrophy, weakness or numbness. It is going to prevent nerve damage as well as relieve those symptoms.”

When performing carpal tunnel release, surgeons can decide if the patient needs to be sedated or if they can receive a nerve block or undergo wide-awake surgery.

“Carpal tunnel release can be performed successfully in a variety of ways, and we have seen an evolution in its surgical treatment generally going from the more invasive to the less invasive. Currently, the common less-invasive techniques include the endoscopic technique vs. mini-open technique,” Ilyas said. “Of late, there has been a move toward beyond just evaluating the surgical technique, but rather how can we treat this in a more efficient manner with less anesthesia and medications.”

However, when it comes to surgery, Ilyas noted that surgeons need to become more responsible for managing patient’s pain postoperatively.

“Frankly, there has not been much evidence for guidelines as the most effective way to manage [postoperative] pain and, generally, we treat pain relatively empirically,” Ilyas said. “We are trying to study patient utilization needs and moving away from over-prescribing medications so as to not both provide too much unnecessary narcotics to both the patient, as well as to not inadvertently deliver excess narcotics into the community for possible diversion or abuse.”

Nonsurgical treatments

According to Ladd, not every patient wants or should undergo surgery for carpal tunnel syndrome.

“We often will get nerve studies that will document the severity of the nerve compression, and that also is an indicator of how severe the disease is and whether [patients] are surgical candidates or can be treated with splinting a little bit longer,” Ladd said. “Maybe [their carpal tunnel] is mild, it may get better on its own or sometimes it is so severe you have to have a meaningful discussion with the patient whether [surgery] is worth doing because the recovery may not be as rewarding as it would be for someone with an early-to-moderate disease.”

Ladd noted modifying the way patients holds their hands during daily activities or wearing a splint can help relieve symptoms of carpal tunnel.

“Sometimes seeing a hand therapist who is adept at what carpal tunnel is and working on not only educating the patient, but maybe there is some other aspect of how they do things they can help correct,” she said. “Particularly, as we get older, patients can have co-existing problems with carpal tunnel syndrome, such as tendonitis and basal thumb arthritis. A therapist is often a person who might realize that there are co-existing conditions and be able to treat those as well.”

Research has shown that steroid injections can also help relieve symptoms of carpal tunnel syndrome.

“I think what people want with carpal tunnel syndrome is something that can modify the course of the disease that is not surgery,” Ring said. “Patients often request a [steroid] injection and they are hoping the injection will solve the problem without surgery.”

But Ring also noted that research on the efficacy of steroid injection is inconsistent.

“The data on carpal tunnel injection with steroids suggests that it can alleviate the symptoms temporarily,” he said. “Some studies show a change in electrodiagnostic characteristics, the nerve function measured electrically; some do not. It is inconsistent.”

Whether the steroid injection helps relieve symptoms in a patient may attest to what the patient’s response to surgery will be, according to Ladd.

“For certain individuals, a steroid injection might help a lot, and a response to steroid injection is often a good indication of someone’s response to surgery,” Ladd said. “Say they have an injection and it gives them relief, albeit temporary. That often is a good sign with a surgical candidate.”

Barry P. Simmons

However, Simmons noted although injections and splints can help with the symptoms of carpal tunnel syndrome, there is no current evidence that suggests the nonsurgical methods can stop the disease from progressing, especially in patients older than 60 years.

He noted a recent study of the long-term follow-up of carpal tunnel release (13 years) disclosed an 88% satisfaction rate; of which 74% reported their symptoms completely resolved. There was only a 1.8% recurrence rate and no complications. Simmons said these results support surgery as the best treatment for older patients with long-standing symptoms, especially those with moderate-to-severe entrapment on EMG/NCS.

“The thing that is important in many cases of carpal tunnel syndrome, especially patients who are older, let us say over 60, with long standing symptoms, meaning 6 months or longer, with significant numbness and with moderate to severe distal latency on electromyography and nerve conduction studies, then surgery is the absolute treatment for those patients,” Simmons said. “Nonsurgical treatments, such as splints, injections, physical therapy, in that group of patients basically does not work.”

Debunked myths

As more research was performed on patients with carpal tunnel syndrome, researchers began to identify risk factors for carpal tunnel and were able to debunk myths about the condition.

“One thing that has been shown to be true in medicine, and I am sure it is true in everything else, is that it takes about a generation to fully debunk a myth even with good science,” Ring said. “I will be the first to admit that we need more data, but I would say that several myths have been debunked.”

Carpal tunnel syndrome was believed to be caused by overuse or repetitive activities, such as typing on a keyboard, but research has begun to show that carpal tunnel syndrome may be genetic.

“[Patients often have the impression] that carpal tunnel syndrome is due to use of their hand,” Ring said. “According to the best available evidence, idiopathic median neuropathy at the wrist is genetic. It is structural and inherent. In other words, it is not related to hand use.”

He noted patients who strongly believe the repetitive hand motions they perform at work is the cause of their carpal tunnel syndrome often have ineffective coping strategies, which can hinder the treatment and healing process.

“If they are absolutely convinced that using a mouse or using a keyboard or doing something over and over on an assembly line is causing harm to their hand, then they have ineffective coping strategies,” Ring said. “Another way that manifests itself is called kinesiophobia, which is fear of motion or fear of use of the hands. People who are claiming that [carpal tunnel] is work-related are more likely to have catastrophic thinking or kinesiophobia, and people who are in that mindset don’t always get back to being able to depend on their hand after surgery.”

Although most surgeons believe carpal tunnel syndrome is not caused by repetitive motion or use of the hands, many patients still strongly believe their carpal tunnel syndrome was caused by excess use. Simmons noted patients still strongly hold this belief because most individuals who have idiopathic carpal tunnel syndrome also have jobs that involve typing or repetitive hand use.

“[Patients] think that computer keyboard use and multiple repetitive motion causes [carpal tunnel syndrome], but the most common age group [who have carpal tunnel syndrome] are the 50-[year-old] to 55-year-old women who will often be the people who have the type of job that involves computer input as well,” Simmons said. “So that is coincidental. That is not related, and there are several studies that show that.”

However, according to Ilyas, research has shown carpal tunnel syndrome is a multifactorial phenomenon, and although repetitive hand motions can aggravate the disease, it is not a direct risk factor for it.

“Among hand surgeons, the myth that just use of the hand such as with typing is the cause of carpal tunnel syndrome has been refuted, but I am not so confident that that myth has been debunked in the general lay population,” Ilyas said. “We now know based upon more rigorous research that [carpal tunnel syndrome] is a multifactorial phenomenon, and although those activities that are considered to be the cause may still aggravate it, the etiology of carpal tunnel syndrome is typically more multifactorial and usually is a combination of age, gender, weight, family history, medical conditions, as well as occupational and recreational exposures which subsequently can put a person at risk for the development of carpal tunnel syndrome.” – by Casey Tingle

Are there epigenetic factors that contribute to carpal tunnel syndrome?

Diagnosis is key

Brent Graham

Despite its common occurrence and familiarity to a broad spectrum of health providers, the etiology of carpal tunnel syndrome remains unknown. The pathophysiologic basis for the symptoms is clearly compression of the nerve, but the cause of this remains obscure. Release of the transverse carpal ligament reliably addresses the symptoms, but this does not necessarily mean that an abnormality of this structure is the primary factor that leads to the clinical syndrome.

Given its prevalence among working-age individuals and the resulting economic impact of the condition, identifying risk factors, especially in the workplace, is obviously desirable and yet this has remained elusive. The reason for this failure to make a clear connection between a workplace exposure and the occurrence of carpal tunnel syndrome may simply be because one does not exist. The condition is so prevalent that linking it to any specific work activity has proven to be difficult. In part this is due to its variable manifestations and the fact that the symptoms may wax and wane even without treatment or changes in activity. However, perhaps even more important, is the fact that the way in which carpal tunnel syndrome is diagnosed varies widely among the clinicians who care for the problem. Consensus on reliable and valid diagnostic criteria for the condition has to be the first step in establishing any association with patient characteristics, either personal traits or workplace activities. It is clear that electrodiagnostic tests alone do not suffice as a tool that meets these requirements. Diagnostic scales to evaluate symptoms do exist and as these become more widely used greater insight into the causes of carpal tunnel syndrome may result.

Brent Graham, MD, MSc, FRCSC, can be reached at the University of Toronto.

Disclosure: Graham reports no relevant financial disclosures.

Causes remain unclear

Warren Hammert

Carpal tunnel syndrome is the most common compression neuropathy in the upper extremity and routinely treated by orthopedists and hand surgeons. Although the diagnosis and treatment options are often clear, the cause may not be.

A number of factors have been associated with carpal tunnel syndrome, and although each individual factor by itself does not cause the syndrome, they may increase the chances of this occurring or her cause an exacerbation of symptoms.

These include:

Anatomical factors: Any condition that alters the space for the median nerve within the carpal tunnel can increase pressure on it, predisposing one to develop symptoms from median nerve compression. Some individuals will have smaller carpal canals, making them potentially more susceptible to anatomical changes within the carpal tunnel. External compression, as can occur with fractures and dislocations by decreasing the size. Alternatively, an increase in the size of the other contents of the carpal tunnel (flexor tendons), as can occur with inflammatory conditions/rheumatoid arthritis, increasing the volume of the contents of the carpal tunnel, creating pressure on the median nerve.

Gender: Carpal tunnel syndrome is generally more common in women, and it is presumed this is due to the smaller size of the carpal canal.

Work-related conditions, such as use of vibratory instruments or substantial repetitive flexion of the wrist, may increase pressure on the median nerve causing carpal tunnel symptoms, but these factors have not definitively been established as a cause of carpal tunnel syndrome. Computer use, keyboarding, playing video games and other repetitive assembly `line activities are often presumed to cause carpal tunnel syndrome. Although symptoms may be exacerbated by any of these activities, there is not high quality evidence suggesting a cause-and-effect for carpal tunnel syndrome. They may cause or be related to other conditions that cause pain in the hand, such as tendonitis.

Warren Hammert, MD, can be reached at the University of Rochester Medical Center.

Although carpal tunnel syndrome is common, noted surgeons who spoke with Orthopedics Today believe there is still debate about the best treatment options for patients and whether there is more about the condition to be discovered.

“The reason that people are willing to take a look at new [treatments for carpal tunnel] is because not everyone is happy after carpal tunnel release,” David C. Ring, MD, chief of hand surgery at Massachusetts General Hospital, told Orthopedics Today. “Some people with advanced disease — constant numbness, weakness, atrophy — those people have permanent nerve damage and it can be very disappointing when they have the surgery and they still have those problems. It does not get better, and so they are unhappy.”

According to Asif Ilyas, MD, program director of the hand and upper-extremity fellowship at the Rothman Institute, carpal tunnel syndrome is a common issue, with studies quoting general prevalence in the 3% to 7% range.

“Carpal tunnel syndrome, in general, is an area of intense research for a number of reasons,” Ilyas, who is also an associate professor of orthopedic surgery at Thomas Jefferson University, said. “One, it is a problem that we as hand surgeons treat very regularly and two, it is a condition that affects a large swath of the population and can significantly affect their lives as well as their livelihood.”

David C. Ring, MD, noted that according to the best available evidence, idiopathic median neuropathy at the wrist is genetic..

Image: Robert Carlin Photography

Research also continues to be warranted on the best way to diagnose carpal tunnel syndrome, which, according to A. Lee Osterman, MD, is still widely debated.

“The optimal diagnosis of carpal tunnel is somewhat debated, whether you rely on just symptoms and signs alone in the physical examination, whether you include electrodiagnostic testing [or] whether you do both,” Osterman, head of the Philadelphia Hand Center and professor of hand surgery and orthopedics at Thomas Jefferson University, said. “Most people still use both clinical examination and the diagnostic tests … but, the American Academy of Orthopaedic Surgeons’ recommendation was, while there was no best scientific evidence to support the use of electro-studies, that they were often helpful.”

Patients who are diagnosed with carpal tunnel syndrome tend to be between the ages of 40 years and 60 years, noted Osterman, although there are some individuals in their 70s and 80s who have fairly severe carpal tunnel that has not been treated. Patients with certain health conditions or who have experienced hand trauma can also suffer from carpal tunnel syndrome.

Amy L. Ladd, MD, chief of the Chase Hand Center and professor of orthopedic surgery at Stanford University Medical Center, noted patients with thyroid disease or those who have had kidney transplants, as well as patients with amyloidosis, are also at higher risk for carpal tunnel syndrome.

“The more common demographic [for carpal tunnel syndrome] is women more than men, although non-exclusively,” Ladd said. “We tend to see it at hormonal fluctuations with women, things like pregnancy, birth control [or] menopause.”

However, Barry P. Simmons, MD, chief of the Hand and Upper Extremity Service at Brigham & Women’s Hospital, told Orthopedics Today 75% to 80% of carpal tunnel syndrome found in women ages 50 years to 55 years is idiopathic. According to Ring, idiopathic carpal tunnel leads researchers to believe that carpal tunnel syndrome is a genetic issue.

“The best evidence for etiology is that [carpal tunnel syndrome] is a genetic problem,” Ring, who is also a professor of orthopedic surgery at Harvard Medical School, said. “The only question left is, ‘Are there any epigenetic factors?’ Is there anything that people do: anything they eat, any activity they do that might increase their risk beyond what their genes have given them? To date, there are no proved epigenetic factors [in idiopathic carpal tunnel syndrome].”

PAGE BREAK

Surgical treatments

Performing carpal tunnel release surgery can help relieve symptoms of carpal tunnel syndrome and can be performed endoscopically or by dividing the transverse carpal ligament, according to Osterman and Ring.

“We understand that the course of [carpal tunnel syndrome] can be modified. You can change the natural history by dividing the transverse carpal ligament,” Ring said. “So if you cut the ligament, the carpal tunnel is bigger and then not only will the symptoms be relieved, but [the patient] will be out of the woods in terms of developing atrophy, weakness or numbness. It is going to prevent nerve damage as well as relieve those symptoms.”

When performing carpal tunnel release, surgeons can decide if the patient needs to be sedated or if they can receive a nerve block or undergo wide-awake surgery.

“Carpal tunnel release can be performed successfully in a variety of ways, and we have seen an evolution in its surgical treatment generally going from the more invasive to the less invasive. Currently, the common less-invasive techniques include the endoscopic technique vs. mini-open technique,” Ilyas said. “Of late, there has been a move toward beyond just evaluating the surgical technique, but rather how can we treat this in a more efficient manner with less anesthesia and medications.”

However, when it comes to surgery, Ilyas noted that surgeons need to become more responsible for managing patient’s pain postoperatively.

“Frankly, there has not been much evidence for guidelines as the most effective way to manage [postoperative] pain and, generally, we treat pain relatively empirically,” Ilyas said. “We are trying to study patient utilization needs and moving away from over-prescribing medications so as to not both provide too much unnecessary narcotics to both the patient, as well as to not inadvertently deliver excess narcotics into the community for possible diversion or abuse.”

Nonsurgical treatments

According to Ladd, not every patient wants or should undergo surgery for carpal tunnel syndrome.

“We often will get nerve studies that will document the severity of the nerve compression, and that also is an indicator of how severe the disease is and whether [patients] are surgical candidates or can be treated with splinting a little bit longer,” Ladd said. “Maybe [their carpal tunnel] is mild, it may get better on its own or sometimes it is so severe you have to have a meaningful discussion with the patient whether [surgery] is worth doing because the recovery may not be as rewarding as it would be for someone with an early-to-moderate disease.”

Ladd noted modifying the way patients holds their hands during daily activities or wearing a splint can help relieve symptoms of carpal tunnel.

“Sometimes seeing a hand therapist who is adept at what carpal tunnel is and working on not only educating the patient, but maybe there is some other aspect of how they do things they can help correct,” she said. “Particularly, as we get older, patients can have co-existing problems with carpal tunnel syndrome, such as tendonitis and basal thumb arthritis. A therapist is often a person who might realize that there are co-existing conditions and be able to treat those as well.”

PAGE BREAK

Research has shown that steroid injections can also help relieve symptoms of carpal tunnel syndrome.

“I think what people want with carpal tunnel syndrome is something that can modify the course of the disease that is not surgery,” Ring said. “Patients often request a [steroid] injection and they are hoping the injection will solve the problem without surgery.”

But Ring also noted that research on the efficacy of steroid injection is inconsistent.

“The data on carpal tunnel injection with steroids suggests that it can alleviate the symptoms temporarily,” he said. “Some studies show a change in electrodiagnostic characteristics, the nerve function measured electrically; some do not. It is inconsistent.”

Whether the steroid injection helps relieve symptoms in a patient may attest to what the patient’s response to surgery will be, according to Ladd.

“For certain individuals, a steroid injection might help a lot, and a response to steroid injection is often a good indication of someone’s response to surgery,” Ladd said. “Say they have an injection and it gives them relief, albeit temporary. That often is a good sign with a surgical candidate.”

Barry P. Simmons

However, Simmons noted although injections and splints can help with the symptoms of carpal tunnel syndrome, there is no current evidence that suggests the nonsurgical methods can stop the disease from progressing, especially in patients older than 60 years.

He noted a recent study of the long-term follow-up of carpal tunnel release (13 years) disclosed an 88% satisfaction rate; of which 74% reported their symptoms completely resolved. There was only a 1.8% recurrence rate and no complications. Simmons said these results support surgery as the best treatment for older patients with long-standing symptoms, especially those with moderate-to-severe entrapment on EMG/NCS.

“The thing that is important in many cases of carpal tunnel syndrome, especially patients who are older, let us say over 60, with long standing symptoms, meaning 6 months or longer, with significant numbness and with moderate to severe distal latency on electromyography and nerve conduction studies, then surgery is the absolute treatment for those patients,” Simmons said. “Nonsurgical treatments, such as splints, injections, physical therapy, in that group of patients basically does not work.”

Debunked myths

As more research was performed on patients with carpal tunnel syndrome, researchers began to identify risk factors for carpal tunnel and were able to debunk myths about the condition.

“One thing that has been shown to be true in medicine, and I am sure it is true in everything else, is that it takes about a generation to fully debunk a myth even with good science,” Ring said. “I will be the first to admit that we need more data, but I would say that several myths have been debunked.”

Carpal tunnel syndrome was believed to be caused by overuse or repetitive activities, such as typing on a keyboard, but research has begun to show that carpal tunnel syndrome may be genetic.

“[Patients often have the impression] that carpal tunnel syndrome is due to use of their hand,” Ring said. “According to the best available evidence, idiopathic median neuropathy at the wrist is genetic. It is structural and inherent. In other words, it is not related to hand use.”

He noted patients who strongly believe the repetitive hand motions they perform at work is the cause of their carpal tunnel syndrome often have ineffective coping strategies, which can hinder the treatment and healing process.

“If they are absolutely convinced that using a mouse or using a keyboard or doing something over and over on an assembly line is causing harm to their hand, then they have ineffective coping strategies,” Ring said. “Another way that manifests itself is called kinesiophobia, which is fear of motion or fear of use of the hands. People who are claiming that [carpal tunnel] is work-related are more likely to have catastrophic thinking or kinesiophobia, and people who are in that mindset don’t always get back to being able to depend on their hand after surgery.”

PAGE BREAK

Although most surgeons believe carpal tunnel syndrome is not caused by repetitive motion or use of the hands, many patients still strongly believe their carpal tunnel syndrome was caused by excess use. Simmons noted patients still strongly hold this belief because most individuals who have idiopathic carpal tunnel syndrome also have jobs that involve typing or repetitive hand use.

“[Patients] think that computer keyboard use and multiple repetitive motion causes [carpal tunnel syndrome], but the most common age group [who have carpal tunnel syndrome] are the 50-[year-old] to 55-year-old women who will often be the people who have the type of job that involves computer input as well,” Simmons said. “So that is coincidental. That is not related, and there are several studies that show that.”

However, according to Ilyas, research has shown carpal tunnel syndrome is a multifactorial phenomenon, and although repetitive hand motions can aggravate the disease, it is not a direct risk factor for it.

“Among hand surgeons, the myth that just use of the hand such as with typing is the cause of carpal tunnel syndrome has been refuted, but I am not so confident that that myth has been debunked in the general lay population,” Ilyas said. “We now know based upon more rigorous research that [carpal tunnel syndrome] is a multifactorial phenomenon, and although those activities that are considered to be the cause may still aggravate it, the etiology of carpal tunnel syndrome is typically more multifactorial and usually is a combination of age, gender, weight, family history, medical conditions, as well as occupational and recreational exposures which subsequently can put a person at risk for the development of carpal tunnel syndrome.” – by Casey Tingle

Are there epigenetic factors that contribute to carpal tunnel syndrome?

Diagnosis is key

Brent Graham

Despite its common occurrence and familiarity to a broad spectrum of health providers, the etiology of carpal tunnel syndrome remains unknown. The pathophysiologic basis for the symptoms is clearly compression of the nerve, but the cause of this remains obscure. Release of the transverse carpal ligament reliably addresses the symptoms, but this does not necessarily mean that an abnormality of this structure is the primary factor that leads to the clinical syndrome.

Given its prevalence among working-age individuals and the resulting economic impact of the condition, identifying risk factors, especially in the workplace, is obviously desirable and yet this has remained elusive. The reason for this failure to make a clear connection between a workplace exposure and the occurrence of carpal tunnel syndrome may simply be because one does not exist. The condition is so prevalent that linking it to any specific work activity has proven to be difficult. In part this is due to its variable manifestations and the fact that the symptoms may wax and wane even without treatment or changes in activity. However, perhaps even more important, is the fact that the way in which carpal tunnel syndrome is diagnosed varies widely among the clinicians who care for the problem. Consensus on reliable and valid diagnostic criteria for the condition has to be the first step in establishing any association with patient characteristics, either personal traits or workplace activities. It is clear that electrodiagnostic tests alone do not suffice as a tool that meets these requirements. Diagnostic scales to evaluate symptoms do exist and as these become more widely used greater insight into the causes of carpal tunnel syndrome may result.

Brent Graham, MD, MSc, FRCSC, can be reached at the University of Toronto.

Disclosure: Graham reports no relevant financial disclosures.

Causes remain unclear

Warren Hammert

Carpal tunnel syndrome is the most common compression neuropathy in the upper extremity and routinely treated by orthopedists and hand surgeons. Although the diagnosis and treatment options are often clear, the cause may not be.

A number of factors have been associated with carpal tunnel syndrome, and although each individual factor by itself does not cause the syndrome, they may increase the chances of this occurring or her cause an exacerbation of symptoms.

These include:

Anatomical factors: Any condition that alters the space for the median nerve within the carpal tunnel can increase pressure on it, predisposing one to develop symptoms from median nerve compression. Some individuals will have smaller carpal canals, making them potentially more susceptible to anatomical changes within the carpal tunnel. External compression, as can occur with fractures and dislocations by decreasing the size. Alternatively, an increase in the size of the other contents of the carpal tunnel (flexor tendons), as can occur with inflammatory conditions/rheumatoid arthritis, increasing the volume of the contents of the carpal tunnel, creating pressure on the median nerve.

Gender: Carpal tunnel syndrome is generally more common in women, and it is presumed this is due to the smaller size of the carpal canal.

Work-related conditions, such as use of vibratory instruments or substantial repetitive flexion of the wrist, may increase pressure on the median nerve causing carpal tunnel symptoms, but these factors have not definitively been established as a cause of carpal tunnel syndrome. Computer use, keyboarding, playing video games and other repetitive assembly `line activities are often presumed to cause carpal tunnel syndrome. Although symptoms may be exacerbated by any of these activities, there is not high quality evidence suggesting a cause-and-effect for carpal tunnel syndrome. They may cause or be related to other conditions that cause pain in the hand, such as tendonitis.

Warren Hammert, MD, can be reached at the University of Rochester Medical Center.